When milling metallic objects downhole, cuttings are generated which must be removed from the wellbore. Cuttings that aren't captured near the milling can go uphole and lodge in undesirable places, such as the BOP rams, flow control devices, and pump liners.
In the past, various types of devices have been used to capture cuttings during milling. One such example is a "Boot Basket," product No. 130-16 offered by Baker Oil Tools. This type of tool relies on the sudden decrease in annular velocity when the cuttings pass the larger O.D. of the boot, reaching the smaller O.D. of the body and the top connection. This slowdown in velocity allows some of the flow to come back around into the basket area where the cuttings can be trapped. Similar tools are offered from Red Barron and are called "junk subs." Other designs are called "globe-type junk baskets" offered by Baker Oil Tools, which comprise a hollow milling head and a double set of free-rotating finger catchers, a middle body, and a top sub. In operation, a core is cut from the formation, and any junk that may have obstructed normal drilling should be recovered above the core. This type of design is primarily used in open-hole, due to its inability to produce any reverse circulating action or vacuum. Hydraulic Junk Basket, product No. 130-73, offered by Baker Oil Tools, provides for movable sleeves which, in turn, rotate a catcher down and under the junk that has accumulated within the body. A similar tool is offered by Houston Engineers Inc. as the H-E Jet Junk Basket. Other types of junk baskets, such as those offered by Bowen, employ reverse circulation. In this type of tool, the flow is directed from inside the tool to the outside, around the bottom, through the junk catcher, and out again through the annular space.
Yet another type of retrieval tool for cuttings is the combination Ball-type Jet and Junk Basket, product No. 130-97, offered by Baker Oil Tools. it uses reverse circulation and coring ability to allow two junk recovery operations in a single run. In the first operation, using high velocity, the tool jet assembly diverts the drilling fluid out of the jet nozzles, down the O.D. of the tool. The fluid goes up through the bottom of the tool and forces any junk items, such as bit cones and hand tools, up into the I.D. of the bushing. The caught debris is held by the catchers attached to the tool. To complete the recovery, the tool is rotated and lowered into the formation to core up any remaining junk. Yet another product offered by Baker Oil Tools is the Jet Bushing, product No. 130-96, which uses high-velocity fluid through the jets to create a vacuum inside the barrel of the tool which causes a reverse circulating effect. The reverse circulation action makes it possible to recover junk without cutting a core. The housing has several junk retention cups so that as the fluid is pumped up the hole, the cups act as internal junk baskets.
As fluid passes over these internal projections, the flow velocity is reduced at the top of each projection, causing the loose junk to be released from the fluid stream. Those cuttings which are not removed from the fluid stream are carried up to the jetting assembly and are either flushed uphole or recirculated downhole. Yet another tool in this area is the M Reverse Circulating Tool, offered by Baker Oil Tools. This tool employs a rubber cup seal that ensures that 100% of the flow going down the drillstring is forced downward on the outside of the junk retrieving pipe. The junk is carried up the inside of the junk retrieving pipe, filtered by a screen, and then the clean fluid is directed out of the tool above the cup. The typical use for this tool is for milling over packers and the milling head is driven by a length of casing rather than drillpipe.
It is an object of the present invention to avoid having to use reverse circulation and, instead, employ through-the-drillpipe circulation to allow the tool to be run with bottom-end tools that have small circulation ports. It is another object of the tool to allow the use of large access ports to efficiently capture the cuttings. This is in distinction to the known designs described above which employed very small ports which limited the ability of the cuttings to enter the cutting retention systems. It is a further object to provide a tool that can be run in any position on the drillstring, as opposed to only on the bottom which is where the prior art designs were located.
Another object of the tool is that it can be run with several of them in series where the first tool removes larger cuttings, and a tool above can remove fine cuttings.